The present invention is in the field of ultraviolet (UV) light sources.
It is known to use ultraviolet (UV) radiation for a variety of uses including those involving the promotion of photochemical reactions and of molecular dissociation.
One problem with known systems is that it is difficult to safely provide sufficient excitation energy to the UV source and difficult to effectively transfer that energy to the substance or entity to be treated. It is therefore difficult to arrange systems for high energy, high throughput industrial purposes.
There is now described an ultraviolet light source which enables efficient, high throughput UV treatment to be conducted. The ultraviolet light source comprises an UV lamp which is excited by a microwave energy source. The lamp is enclosed by a waveguide comprising UV transparent material. The ultraviolet light source is particularly suitable for the treatment of liquids which are flowed past the ultraviolet light source.
According to one aspect of the present invention there is provided an ultraviolet light source comprising an ultraviolet bulb; a microwave energy source for exciting said ultraviolet bulb; and an enclosure for enclosing the ultraviolet bulb, the enclosure comprising an optically transparent waveguide.
The dominant wavelength of the ultraviolet light source is either
(a) from 140 to 240 nm, preferably from 150 to 220 nm, most preferably from 160 to 200 nm, particularly 182 nm or 185 nm and the ultraviolet light source is suitable for use in promoting molecular dissociation reactions; or
(b) from 300 to 400 nm, preferably from 320 to 380 nm, most preferably from 330 to 370 nm, particularly 346 nm and the ultraviolet light source is suitable for use in promoting photochemical reactions.
By optically transparent waveguide it is meant a waveguide that is substantially transparent to the ultraviolet radiation employed herein, typically having a transparency of greater than 50%, preferably greater than 90% to UV radiation.
The waveguide controls the flow of ultraviolet radiation from the enclosure. The control function typically includes the prevention of the release of harmful or unnecessary ultraviolet radiation frequencies. The exact nature of the waveguide and its control function can be tailored to fit the purpose of use.
Suitably, the ultraviolet bulb has no electrode. That is to say it is an electrode-less bulb such as one comprising a partially evacuated tube comprising an element or mixtures of elements in vapour form. Mercury is a preferred element for this purpose, but alternatives include mixtures of inert gases with mercury compounds, sodium and sulphur. Halides, such as mercury halide are also suitable herein. Amalgams are also suitable herein including indium/mercury amalgam.
In one aspect, the waveguide controls the flow of microwave energy from the enclosure. Control of the microwave energy which passes through the waveguide is useful in embodiments of the invention which make use of both UV and microwave radiation.
In another aspect, the waveguide blocks at least the majority of the flow of microwave energy from the enclosure.
Suitably, the enclosure comprises quartz or a UV-transparent plastic material.
Suitably, the enclosure is coated with a coating which assists in controlling the flow of ultraviolet and/or microwave energy therefrom. The coating may be applied to either or both of the inner or outer surfaces of the enclosure. Partial coatings are also envisaged.
Suitably, a system for cleaning the enclosure (e.g. the quartz tube) is incorporated herein. Suitable cleaning systems include those based upon fluid flow, such as flow of water, air or gas. Cleaning agents such as detergents may be employed as necessary.
Suitably, the waveguide comprises a conducting material. The conducting material may be integral, or applied as an internal or external coating or liner. The liner may directly contact the inner surface of the enclosure or be spaced therefrom.
Suitably, the waveguide comprises a conducting mesh. Preferably, the conducting mesh comprises a high frequency conducting material selected from the group consisting of copper, aluminium and stainless steel.
The ultraviolet bulb has any suitable shape and size, including elongate forms such as a cigar-shape. The bulb size can be tailored. Typical bulb diameters are from 5 to 200 mm, for example 38 mm.
Embodiments are envisaged in which plural bulbs are employed. The bulb may be similar in type e.g. of similar size and operating temperature or combinations of different bulb types may be employed. The number of bulbs employed is tailored to the purpose of use. Typically from 2 to 25 bulbs are employed, such as from 3 to 18 bulbs. Various forms of arrangement of the plural bulbs are envisaged including random or informal arrangements, side-by-side arrangements, sequential arrangements, array arrangements and clusters. The bulbs may be arranged in serial, parallel or mixed serial and parallel electrical circuit arrangements.
The optically transparent waveguide has any suitable shape, such as cylindrical or rectangular forms. The length and size of the waveguide is tailored to fit the particular purpose of use and to accommodate the necessary bulb(s).
Suitably, the ultraviolet bulb has an operating temperature which maximises the chosen bulb characteristics. Typical operating temperatures are from 10xc2x0 C. to 900xc2x0 C., and the operating temperature will be selected and optimised according to the purpose of use.
Suitably, the microwave energy source comprises a magnetron. Alternative sources are envisaged such as solid state devices.
Suitably, the ultraviolet light source additionally comprises a system for cleaning the enclosure.
Suitably, the ultraviolet light source additionally comprises a pathguide to guide the microwave energy from the microwave energy source to the ultraviolet bulb.
In one aspect the pathguide defines an essentially linear path for the microwave energy.
In another aspect, the pathguide defines a non-linear path such as a path defining an angle, such as a right angle.
Suitably, the pathguide comprises a coaxial cable.
Suitably, the ultraviolet light source additionally comprises a housing for said enclosure. Preferably, the housing has an inlet and an outlet and the housing is shaped to guide fluid flow from the inlet, past the enclosure to the outlet. Preferably, the fluid comprises air or a liquid such as water. Suitably, the ultraviolet light source additionally comprises a pump for pumping fluid from the inlet, past the enclosure to the outlet. Alternatively, gravity may be utilised to encourage fluid flow.
The choice of materials for use in the housing and any fluid flow piping arrangements can be important. Typically, the materials will be selected which are resistant to corrosion and which do not leach contaminants to the system.
Seal materials are also carefully selected with typical seal materials including Chemraz (trade name), Teflon (trade name), encapsulated Viton (trade name) and GORE-TEX (trade name).
According to another aspect of the present invention there is provided a lamp comprising an ultraviolet bulb, said bulb being excitable by microwave energy; and an enclosure for enclosing the ultraviolet bulb, the enclosure comprising an optically transparent waveguide.
The dominant wavelength of the lamp is either
(a) from 140 to 240 nm, preferably from 150 to 220 nm, most preferably from 160 to 200 nm, particularly 182 nm or 185 nm and the lamp is suitable for use in promoting molecular dissociation reactions; or
(b) from 300 to 400 nm, preferably from 320 to 380 nm, most preferably from 330 to 370 nm, particularly 346 nm and the lamp is suitable for use in promoting photochemical reactions.
Preferably, the ultraviolet bulb has no electrode.
According to a further aspect of the present invention there is provided a method of promoting the dissociation of a molecular entity comprising
applying microwave energy to an ultraviolet lamp to produce ultraviolet radiation of dominant wavelength of from 140 to 240 nm; and
exposing the molecular entity to said ultraviolet radiation, wherein
an enclosure encloses the ultraviolet lamp, the enclosure comprising an UV transparent waveguide.
In one aspect, the molecular entity is borne in a fluid such as air or a liquid and the fluid flows past the enclosure. A specific example of this is in the clean up of ballast seawater from the holds of ships wherein contaminants in the ballast water are dissociated by application of ultraviolet radiation.
A further specific example of molecular dissociation applications based on fluid flow is in the dissociation of organic material, such as Total Oxidisable Carbon (TOC) in rinse water for use in the electronics, semiconductors pharmaceuticals, beverage, cosmetics and power industries. The process involves the production of OH.radicals which oxidise any hydrocarbon molecules in the rinse water. Optionally, other oxidants may be employed such as ozone and hydrogen peroxide. Typically, polishing deionisation beds, featuring nuclear-grade resin materials are placed downstream of the TOC reduction units to remove any ionised species and restore the resitivity of the water.
In another aspect, the molecular entity is borne on a surface and the ultraviolet radiation is applied to the surface. The molecular entity may, for example be a contaminant on the surface which is rendered harmless by its molecular dissociation.
In one example, the surface is of a food product such as a meat, dairy, fish, fruit or vegetable product and the ultraviolet radiation is applied to the surface to dissociate any contaminants such as chemical residues including pesticides.
In another example, the surface is an industrially-produced product such as a packaging product for example, a medical packaging product, a foil bag, cup or lid, or a glass or plastic bottle, and the ultraviolet radiation is applied to the surface to dissociate any contaminants arising from the industrial process.
In a further example, the surface is the surface of any equipment used in the manufacture of food products or industrially produced products such as the surface of any reactors or conveyors.
According to a still further aspect of the present invention there is provided a method of promoting a photochemical reaction in a substance comprising
applying microwave energy to an ultraviolet lamp to produce ultraviolet radiation of dominant wavelength of from 300 to 400 nm; and
exposing the entity to said ultraviolet radiation, wherein
an enclosure encloses the ultraviolet lamp, the enclosure comprising an UV transparent waveguide.
In one aspect, the substance is borne in a fluid such as air or a liquid and the substance-bearing fluid flows past the enclosure.
In another aspect, the substance is borne on a surface and the ultraviolet radiation is applied to the surface.
Preferably, the substance is selected from the group consisting of surface treatment materials including paints, toners, varnishes (e.g. polyurethane varnishes), stains and laminating materials.
Laminating is for example, used in the production of various electronic components, data storage devices including compact discs and packaging materials including blister packages.
According to a further aspect of the present invention there is provided an ultraviolet light source comprising a plurality of ultraviolet bulbs; a microwave energy source for exciting said plurality of ultraviolet bulbs; and an enclosure for enclosing the plurality of ultraviolet bulbs, the enclosure comprising an optically transparent waveguide.
According to a further aspect of the present invention there is provided a lamp comprising a plurality of ultraviolet bulbs, said plurality of bulbs being excitable by microwave energy; and an enclosure for enclosing the plurality of ultraviolet bulbs, the enclosure comprising an optically transparent waveguide.